1. Field of the Invention
The present invention relates to data telecommunications and more particularly to data telecommunications over the wide-area analog telephone network.
2. State of the Art
The analog telephone network by its nature uses analog electrical signalling over copper wire between a central office and customer telephone sets. Computer communications, being based on digital signalling, require an analog to digital conversion to be performed in order to support digital communications over the analog phone network. This conversion is typically done by a modem (modulator/demodulator). This approach is adequate for basic digital data communications, and has been employed for the last several decades. A typical modem consists of a digital signal processor (DSP), a hybrid 2/4 wire interface, a codec, a microcontroller to manage system functions, and a serial interface to the computer, typically using the RS232C signalling approach with ASCII encoding.
There are significant disadvantages to this approach. By embedding the entire communications and signal processing functionality in an external device, a lower bound is placed on the cost of the device. Furthermore, the RS232C/ASCII signalling convention precludes access to non-digital (analog) signals that may be carried on the telephone network. Direct access to a digital representation of the analog channel is required for voice recognition, text-to-speech conversion, proprietary encoding of video signals, and other related technologies. Finally, conventional modems do not allow for adaptation to the various international telephone standards, requiting instead replacement of the entire modem.